To meet a recent demand for high speed and high integration of a semiconductor device and high miniaturization of a wiring pattern thereof, a copper (Cu) multilayered wiring technology is attracting attention. In this technology, copper, which has high conductivity and high electromigration resistance, is used as a wiring material, and a low-dielectric film (Low-k film) is used as an interlayer insulating film.
As a method for forming a copper wiring, there is known a technique in which a barrier layer made of, for example, Ta, TaN or Ti is formed on an interlayer insulating film having a trench or a hole by a physical vapor deposition (PVD) method; a ruthenium film as a liner film is formed on the barrier layer by a chemical vapor deposition (CVD) method; and a copper film is formed on the ruthenium film by the PVD method (see, for example, Patent Document 1). The ruthenium film formed by the CVD method has higher step coverage than that of a ruthenium film formed by the PVD method and, also, has high adhesivity with the copper film. Thus, this ruthenium film has advantages as an underlying film when burying the copper film in the trench or the hole.
As a technique for forming the ruthenium film by the CVD method, there is proposed a method of using ruthenium carbonyl (Ru3(CO)12) as a film forming source material, while using an Ar gas as a carrier gas and using a hydrogen gas as a reducing gas (see, for example, Patent Document 2). Further, there is also proposed a method of using ruthenium carbonyl as a film forming source material and carbon monoxide (CO) as a carrier gas (see, for example, Patent Document 3). In a reaction system using the ruthenium carbonyl and the carbon monoxide, since impurity components in the film forming source material are restricted to carbon and oxygen, a film having high purity can be formed. Further, there is also proposed a method of using ruthenium carbonyl as a film forming source material and reducing the amount of residual carbon in a formed ruthenium film by performing annealing under a hydrogen gas atmosphere after the ruthenium film is formed (see, for example, Patent Document 4).
Moreover, though not related to a ruthenium film forming method, there is also proposed a method for reducing the amount of impurities in a film. In this method, by repeating a TiN film forming process of forming a TiN film to be used as an electrode for a storage node by using TiCl4 as a source material and a treatment process under an ammonia gas atmosphere, the component of chlorine in the TiN film is reduced (see, for example, Patent Document 5). Furthermore, there is also known a by-product removal accelerating method. According to this method, in depositing a metal film by thermal decomposition of a metal carbonyl precursor, by repeatedly exposing the metal film to a reducing gas such as SiH4, BH3 or NH3 during the formation of the metal film, the removal of the by-product introduced into the metal film is accelerated (see, for example, Patent Document 6).
In addition, also proposed is a technique of adding ammonia to a process of forming a HfB2 film by the CVD method (see, for example, Non-patent Document 1). According to this method, it is deemed that nucleation is homogenized in the growth of the HfB2 film by using the ammonia as the inhibitor and, thus, a smooth HfB2 film can be formed.
Patent Document 1: Japanese Patent Laid-open Publication No. 2012-169590
Patent Document 2: Japanese Patent Laid-open Publication No. 2008-514814
Patent Document 3: U.S. Pat. No. 7,482,269
Patent Document 4: Japanese Patent Laid-open Publication No. 2010-212601
Patent Document 5: Japanese Patent Laid-open Publication No. 2008-091899
Patent Document 6: Japanese Patent Laid-open Publication No. 2007-507613
Non-patent Document 1: Growth Inhibitor To Homogenize Nucleation and Obtain Smooth HfB2 Thin Films by Chemical Vapor Deposition, Chemistry of Materials 2013, 25, p662˜667.
Recently, as a design rule of a semiconductor device is getting more miniaturized, a copper multilayered wiring structure is also getting miniaturized. In order to improve an operating speed of the semiconductor device and a signal transmission speed of the copper wiring while achieving the miniaturization thereof, it is required to suppress a RC delay. One of solutions for suppressing the RC delay is to reduce resistance of the wiring. As one of directions for achieving the low resistance of the copper wiring, it is deemed to be effective to maximize a volume of the copper wiring buried in a trench or a hole. To maximize the volume of the copper wiring, it is required to set a total thickness of a barrier film and a liner film to be as small as possible.
In the CVD method, however, if a thickness of the ruthenium film is reduced to, for example, 2 nm or less, the ruthenium films becomes discontinuous and may not exert a function as a liner film, so that a poor burial, such as a void, is generated in the copper wiring. In this regard, it is difficult to form a continuous ruthenium film in a thickness equal to or smaller than, e.g., 2 nm by the conventional CVD method, which may become a hindrance to achieving the low resistance of the copper wiring.